Sound recording device



Jan. 4,' 1938. K. SCHWARZ 2,104,170

SOUND RECORDING DEVICE Filed Nov. 13, 1955 INYVENTQR A KARL SCH/V432 I #im ATTORNEY Patented Jan. 4, 1938 UNITED STATES PATENT OFFICE SOUND RECORDING DEVICE Application November 13, 1935, Serial No. 49,465

. In Germany April 15, 1935 Claims.

This invention relates to signal recording devices such as that disclosed in my copending application Serial No. 28,418, filed June 26, 1935 (D10,191), and has for its principal object the 5 .provision of an improved signal recording mechanism and method of operation whereby a recording element, such as a galvanometer mirror or the like, is vibrated about one axis in accordance with the signal to be recorded and is rortated about another axis in accordance with the signal volume. The present invention involves features similar in some respects to those disclosed by a copending application of EdwardW. Kellogg, Serial No. 531, filed Jan. 5, 1935 and assigned to Radio Corporation of America but differs therefrom in the constructional details and operating principle of recording mechanism.

The object of the copending application (Serial No. 28,418) is the provision of a method and means adapted to produce variable area type records that are free from background noises. To this end a stationary serrated diaphragm or light-stop serves to contour and bound a light pencil or beam, which is caused to impinge upon a mirror oscillated about an axis or pivot at the frequency of the signal, the said pivot being positioned perpendicularly at right angles to one of the edges of the stop. This mirror is also moved in response to the signal volume current about another pivot positioned at right angles to the other edge of the stop. The two axes about which the mirror must be caused to oscillate according to the method disclosed in the aforesaid copending patent application, thus form an angle relative to each other which is equal tothe angle formed between two abutting edges of the multitooth mask or light-stop. In the case where the edges of the multi-serrated light-stop are at right angles to one another; the oscillating mirror, as will thus be seen, must be pivotable about two axes-being at right angles to each other. This special requirement is somewhat dimcult of fulfillment because the space available for the device is limited and replacement of the light valve 5 in the sound recorder apparatus is likely to be required. 5

In addition to the difliculties just outlined, there are others which are due to the requirement that the center of the mirror should occupy 50 a definite position upon the optical axis, and that the mirror plane, in its zero position, should be in a definite position with'respect thereto.

According to the present invention, these difiiculties are obviated in that the mirror is supported by a string, chord or other suitable memher which admits of rotational movements of the mirror about the longitudinal axis of the string support and in that the mounting and adjusting means for the string support and the mirror are rotatable about an axis which forms with the string support an angle that corresponds to the diaphragm angle. This new arrangement makes it possible to effect adjustment of the mirror in the sense of the difierent coordinates essentially independently of one another. Inasmuch as the 10 mirror involves very little inertia, it is preferable that the mirror should be excited about the string sup-port in accordancewith the signal vibrations. The supporting and adjusting system involves far more inertia and is less suited and 5 able to follow the tonal oscillations. In fact, this system is called upon to experience comparatively slow vibrations, say, up to around 20 cycles per second. These oscillations are due to fluctuations of the direct current generated by rectification of the signal currents, the intensity of which corresponds to the volume of the sound or signal to be recorded and is subject to but slight alterations in comparison with the tonal vibrations.

Inasmuch as it is necessary to provide a magnet in whose field the mirror excited at tonal frequency is capable of oscillating, and since this magnet would greatly increase the weight of the system which is to vibrate in unison with the signal volume current, means are provided which 30' 'with the signal amplitude or volume, whereas the magnet itself remains at rest. This yielding union 40 between the pole-shoes and the magnet, however, must be chosen in sucha way that the magnetic flux in the pole-shoes will be large. It is therefore suggested to choose a'high-permeability material throughout the pole-shoes, and to so taper the same at one place that the pole-shoes can, be readily bent in accordance with the oscillations of the supporting system. However, the same end is attainable in that the pole-shoes. terminate at their ends or tips in a plate or blade of magnetic material, and that the latter is connected with the magnet with the interposition of a tenuous layer of yielding or flexible mateterial such as rubber or the like. While this meansa small'gap between the pole-shoe and the magnet filled with material of low permeability, the magnetic flux in the pole-shoes will nevertheless be of the requisite intensity on the ground that the cross-sectional area at this place is conveniently large.

The magnet, preferably a bar magnet, is disposed below the supporting system, and the same has a central bore through which the driving system of the noise control means may be shifted and made to engage. Screwed upon the ends of the bar magnet are blocks or resting means in Which the flexible pole-shoes may be fastened by clamping action or upon which the said layer of rubber may be arranged. Owing to the fact that the said supporting blocks are screwed on, this allows adjustment of the center of the mirror. In fact, by shifting the same conditions can be made so that the center of the 'mirrorwill coincide with the optical axis. I

For driving and adjusting the supporting sys tem there serves 'preferably'an electromagnetic system which is subject to a control action'produced by a current which is responsive to the signal amplitude or volume. For this purpose there is rigidly associated with the supporting system a ferro-magnetic body which is hereinafter called a tongue or reed whose free end is capable of oscillating in front of the pole-shoes of a magnet."

This driving system is preferably designed so as to act as a so-called free oscillator. The exciting coil embraces at one end the said tongue, while; at the other end it is seated in a ring magnet upon the ends of which pole-shoes are screwed fast, which bound an air-gap in the middle of" the magnetic ring and in which, as stated, the said.

tongue is capable of vibrating.

The supporting system could comprise either a' knife edge system or a mechanical pivot 01'' else be insured by supporting in more than one point, provided that, upon eifecting a shift in these supporting points, at least approximately rotation of the supporting system about .the desired axis passing through the mirror is insured.

According to another aspect of this invention,

the supporting system bears upon leaf springs the ends of which are capable of rotational movements about their clamping or securing point. In 7 serves' to adjust the entire vibrational system in reference to the casing of the light valve. The securing of the leaf springs must be accomplished with a good deal of care in order that the rotational movements about the desired axis or pivot may result. The leaf springs are locked in position by screws which in case they have not been completely tightened allow of a certain amount of clearance or play between the springs and the body. When adjusted,'these screws are tightened and leaf springs and body are connected by pins or tenons in that, after adjustment has been perfected, leaf springs and body are drilled, whereupon a pin is introduced into the bore hole; After the adjustment of the support- .may be effected in various ways.

ing system in relation to the exciting means for the noise reduction currents effected in a way as stated, the device is inserted into the casing of the light valve so that it will thus be protected in a dust-proof and hermetical way. By the aid of pressure (thrust) and tractile screws, the position of the oscillation system in reference to the casing can be adjusted in any desired direction.

The sequence in which the various adjustments ,must be accomplished, and more particularly in what Way the system oscillating at tonefrequency must be constructed is described below in more detail by reference to the drawing illustrating one exemplified embodiment of the invention.

Referring to the drawing,

Fig. 1 shows asection laid through the light valve at right angles to the axis about which the signal volume responsive oscillations take place,

Fig. 2 shows a section at right angles to the other axis of rotation of the mirror about which the signal, responsive vibrations take place, the' casing having been omitted'in this figure.

Fig. 3 is a View of the light valve in the direction of the optical axis after removal, of casing, and

chord or string of theoscillating mirror.

-The oscillatingmirror I (Fig. '3) is supported by a chord 2. In order "to facilitate and simplify the fastening of the mirror in reference to the chordas well as'the clamping of the latter, 'a chord having rectangular cross-sectional'shape as shown in Fig. 4 is used. The clamping and locking of the chord in the supportingsystem 3 Thusat both ends of the chord, bolts 4 provided with grips 5 may be provided. These bolts may be sawed open so that the chord may be inserted, and then the parts may be secured in reference to each other by suitable clamp screws. By means of guide pins 28 which are seated in one-half'of the bolt and engage in bores 29 of the other half of the bolt, relative slipping of the bolt members or halves is prevented; By changing the relative distance of the bolts, the, free length of the chord is alterable and thus also the natural period of the oscillatory system comprising the chord and the mirror.

The'oscillatory system' is subject to 'a driving screwed upon the bar magnet 9. Two types of pole-shoe mounting according to this invention are illustrated inEig. 2. The lefthand pole-shoein Fig. 2 terminates in'a platelet lll disposed on the block 8 with interposition of a rubber disk or washer II. The right-hand pole-shoe shows a leaf spring I2 which permits thepole-shoe of;ex periencing movements in reference to the block.

Also at this place a rubber buffer is interposed as indicated at H. The rubber. disk ll serves to dampen or deaden the vibrations of the leaf spring l2. Also thelayer of rubber on the lefthand pole-shoe has this effect.

Adjustment of theinatural period of oscillation of the mirror is effected by adjusting the free length of the chord or string which may be altered by means ofthe ends or. grips 5. By shifting the.

bolts 4 in the same sense the centerof the. mirror may be alined with theoptical axis. However,

it is by .no means necessary to make the clamp- Fig. 4 illustrates the mode of clamping the ing or securing means for the mirror symmetric. In fact, in some instances it may be preferable to fasten one end of the string in a leaf spring, and to render the opposite end adjustable. When the proper position for the center of the mirror has been ascertained, care is required to orientate the face of the mirror properly with respect to the chord acting as the axis of rotation. This may here be effected by turning the bolts in the clamping device. After also this setting has been accomplished, then the bolts are locked by a screw provided in the supporting system.

The bar maget 9 has a central bore which provides room for a tongue l3 which is fastened on the supporting system 3. The lower end of the tongue is oscillated under the influence of the changing magnetic field between the pole-shoes I4 of a ring magnet l5. This alternating field is created by the signal volume or amplitude responsive currents in a coil IS. The oscillations of the supporting system and thus of the mirror are made possible by the leaf spring supports l'l. These oscillations are damped or deadened not only by the said rubber buffer means between pole-shoe 6 and upright or block 8, but in addition damping or buffer means may be interposed also between the bar magnet 9 and the tongue l3, as indicated at l8.

Disposed on the ring magnet I is a body l9 against which the leaf springs I! are clamped by the screws 20. After final adjustment, pin or tenon connection is effected by the aid of pins 2|. The leaf springs I1 terminate in knife edges at their free ends which engage in the bearing 22 of the supporting system. The suporting system 3 is provided with openings 23' through which chords (not shown) are passed for ensuring that the supporting system stop properly bears upon the knife edges. Adjusting and guide screws 24 and 25 respectively, are arranged in body IS. The screws are so set that the heads thereof are in a plane which is parallel to that of the face of the mirror I. At the bottom of the case a cover 26 is screwed off, the light valve is fitted into the case and is fastened on the latter by means of tractile screws 25, and finally the bottom 26 is fitted on again. By tightening or loosening the screws 25, it is feasible to set the face of the mirror exactly parallel to the fiat surface 21 of the casing. Inasmuch as the last-mentioned surface, after inserting, is pressed against a matching surface of the optional means, exact adjustment of the mirror face will be insurable in spite of the fact that the device is entirely encased.

In lieu of rubber, of course, also other suitable yielding substances may be employed, provided that they involve sufficient internal friction.

I claim:

1. The combination of an assembly comprising a vibratable member, electrical signal responsive means operable to vibrate said member about one axis, resilient means supporting said assembly, and electrical signal volume responsive means coupled to said assembly and operable to vibrate said assembly about another axis.

2. The combination of a galvanometer assembly comprising an electromagnetic element, a mirror vibratable about one axis in accordance with the energization of said element, an auxiliary electromagnetic element, resilient supporting means interposed between said assembly and said auxiliary electromagnetic element, and coupling means connected between said assembly and said auxiliary electromagnetic means for moving said mirror about another axis in accordance with the energization of said auxiliary electromagnetic element.

3. A signal recording mechanism of the galvanometer type including a magnetic structure, pole-shoes resiliently supported on said structure, electrical signal responsive coils cooperatively associated with said pole members, and a flexibly supported vibratable member interposed between said pole-shoes.

4. A signal recording mechanism of the galvanometer type including a magnetic structure, pole-shoes resiliently supported on said structure and tapered at their opposed ends, electrical signal responsive coils cooperatively associated with said pole members, and a flexibly supported vi- 7 bratable member interposed between said poleshoes.

5. In a signal recording mechanism, the combination of electrical signal responsive means in cluding an electromagnetic structure provided with an opening and a member vibratable about one axis in accordance with the energization of said means, an auxiliary electromagnetic responsive means coupled to said member through said opening and operable to vibrate said member about another axis.

KARL SCHWARZ. 

